A cryogenic Paul Trap for highly charged ions

Forbidden optical transitions in highly charged ions (HCIs) are excellent candidates for high stability frequency standards due to their low susceptibility to external influences. Certain lines in HCIs can be used to stringently test the hypothesized time evolution of fundamental constants due to a enhanced sensitivity to variations of the fine structure constant. Quantum electrodynamic effects as large as 1 % of the transition energy, and nuclear size effects of a few percent (e.g., in the hyperfine structure of heavy hydrogenic ions) are found in such transitions. However, such high accuracy experiments require HCIs at rest in space, i. e. they need to be trapped and cooled. A broad range of HCIs can be sympathetically cooled using a (Be+) ion cloud trapped in a Paul trap.

CAD drawing of the CryPTEx set-up

A Cryogenic Paul Trap Experiment (CryPTEx)

To reduce the background pressure and to increase the ion lifetime the Paul Trap is maintained at liquid Helium temperature (~4 K). At this temperature almost all gases will stick to the walls of the vacuum chamber. This results in a very low background pressure of about 10-12 mbar. Optical access is provided via temperature-shielded optical viewports in the horizontal plane.

Solid state laser system at 313nm

Laser cooling of beryllium ions requires laser light at 313nm wavelength. This light is obtained by first summing the frequencies of 1050nm and 1550nm fiber lasers in a PPLN crystal; the resulting light at 626nm is doubled in cavity enhanced SHG to 313nm. The laser system is nearing completion at the PTB where we work together with the QUEST group of Piet Schmidt.